AVR Freaks

The same PORT pin is used as Input Capture also for Tacho speed measurement.

/* TACHO (ATMega8 at 8 MHz) 
  todo- 1.set dia 2.i2c-belt speed & pulse count to main board by I2C	*/

#include <inttypes.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/eeprom.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
//#include <twi_slave.h>
//#include <util/atomic.h>


#define		GRN_on 	 	PORTD &= ~(1<<3);
#define 	GRN_off		PORTD |= 1<<3;

#define		RED_on 	 	PORTD &= ~(1<<4);
#define		RED_off		PORTD |= 1<<4;

	
 

volatile unsigned char  update,tick,flash,tacho_block,seconds;
volatile unsigned char  *tx_char,Tx_Buffer[80],Rx_Buffer[20],*Rx_char,Rx_Wr_Index,serial_transmit;

volatile signed int	tacho_pulse,circumference,Timer_val,period,rev,tacho_speed,diameter;

	



void update_delays(void);
void tacho_input(void);
void belt_speed(void); 

void uart_txn(void);
void uart_data(void);
void string_transfer(void);
void USART_Init(void);


SIGNAL(SIG_OVERFLOW2)							//timer 2 overflow  isr
{
	cli();
	TCNT2 = 0x00;						//7D;							
	tick++;
	update = 1;	
	sei();
}
	
ISR(TIMER1_CAPT_vect)
{
	cli();
	Timer_val = ICR1L;
	Timer_val|=(ICR1H<<8);	
	TCNT1 = 0;
	
	//tacho_pulse++;
	sei();
	
}	


int main(void)
{	
	DDRB = 0xFC;				//FE
	PORTB = 0xFE;				//FE
	
	DDRC = 0x00;													
	PORTC = 0x00;										
	
	DDRD = 0xFF;			//0xC2;  0x82B				// PortD,2to 5 input keys of display,D6 &D7 as as Input enable 
	PORTD = 0xFF;	
	
	OSCCAL = eeprom_read_word(0x0000);		//set OSCCAL to Freq CAL value at 8 MHz
	
	//ADCSRA = 0x07;							// ADC  prescalar--8MHz/64 = 125KHz
	//ADCSRA = (ADCSRA |0x98);					// ADC  Set ADEN,ADIF & ADIE	
	
	TCCR2 =  (1<< CS20)|(1<< CS21)|(1<< CS22);				//Timer 2 settings;	prescaler: f = 8Mhz, fixed to 1/1024	= 7812.5
	TIMSK = (1<<TOIE2);					//sbi(TIMSK, TOIE2); enable timer 2 interrupt
	
	TCCR1A = 0;TCNT1=0;							//// Input Capture Pin Setup; 16 bit counter to  zero	
	TCCR1B |= (1<<ICES1)|(1<<CS10)|(1<<CS12);	// get rising edge first; prescale to 1024;			last was 256	
	TIMSK |= (1<<TICIE1)|(1<<TOIE1);	// enable ICP interrupt; enable timer 1

	
	sei();
	//i2c_init();
	//TWI_slave_init();
	USART_Init();
	diameter = 300;
		
		
	
	
	__main:
	update_delays();
	uart_txn();
	tacho_input();
	belt_speed();
	
	goto __main;	
}



void update_delays(void)   
{
	if(update == 1)
	{
		if(tick > 30)   						//112				 		
		{
			tick = 0;
			flash = 1-flash;
			if(flash ==1)
			{
				RED_on		
			}
			else
			{
				RED_off
			}	
			
			serial_transmit = 1;
				
			/*seconds++;
			if(seconds > 5)
			{
				seconds = 0;				
				serial_transmit = 1;
			}	*/				
		}		
		update = 0;				
	}
}	

void tacho_input(void)
{
	if(((PINB)&(0x01))==1)						//if(((PINB) & (0x01))!=0)
	{
		if(tacho_block == 0)
		{
			tacho_block = 1;
			tacho_pulse++;		
			
		}
		GRN_on				
	}
	else
	{
		tacho_block =0;
		GRN_off
	}

	
}	
	
void belt_speed(void)
{
	circumference = 31.429*diameter;				// circumference x 10 for accuracy calc
	period = Timer_val*1.28;						// freq/1024 = 7812.5 Hz; 1/7812.5 is period of one pulse on Timer = 0.128mSec
	rev = (100000/period);						//rev x 10 for accuracy calc
	tacho_speed = (circumference/1000)*rev;		// speed x 100 	for accuracy calc
	if(tacho_speed < 1)							// to avoid speed in  7 digit figure when stationary
	{
		tacho_speed = 0; 
	}
	/*		
	

	tacho_speed_lo = tacho_speed & 0xFF;		// low
	tacho_speed_hi = (tacho_speed >>8);
	
	write_data[0] = tacho_speed_lo;
	write_data[1] = tacho_speed_hi;	
	
	tacho_pulse_lo = tacho_pulse & 0xFF;		// low
	tacho_pulse_hi = (tacho_pulse >>8);
			
	write_data[2] = tacho_pulse_lo;
	write_data[3] = tacho_pulse_hi;			*/

}		



/*-------------------------------UART------------------------------------------------------------------*/
void uart_data(void)
{
	sprintf(Tx_Buffer,"Dia:%d Pulse:%d circum:%d period:%d rev:%d Speed:%d",diameter,tacho_pulse,circumference,period,rev, tacho_speed);	
	tx_char = Tx_Buffer;	
}


void uart_txn(void)	
{
	if(serial_transmit == 1)
	{
		uart_data();	
		string_transfer();

		serial_transmit = 0;	
	}
}	

void string_transfer(void)
{
	int i;	
	for (i=0; tx_char[i]!='\0'; i++)		// transfer the string
	{ 
		while(!(UCSRA & (1<<UDRE)));	
		UDR = tx_char[i];
		
	}
	while(!(UCSRA & (1<<UDRE)));	
	UDR = 0x0D;								// carriage return 	(to home position)
	while(!(UCSRA & (1<<UDRE)));	
	UDR = 0x0A;								// line feed		(next line)
}	

/*SIGNAL(SIG_UART_RECV)
{
	Rx_char = UDR;
	Rx_Buffer[Rx_Wr_Index] = Rx_char;
	Rx_Wr_Index++;	
	//Rx_cntr++;	
}	*/
	
void USART_Init(void)
{	
	UBRRH = 0;					//Set baud rate       UBRR = (fOSC/16*BAUD) - 1;  then change to hex code
	UBRRL = 0x03;				//set for 115200 baud
	
	UCSRA = 0;	
	//UCSRB = (1<<TXEN)|(1<<RXEN)|(1<<RXCIE);
	UCSRB = (1<<TXEN);
	UCSRC = (1<<URSEL)|(1<<UCSZ1)|(1<<UCSZ0); 			//8bit data,  Zero parity , 1 stop bit
}	
	

Kartman wrote---circumference and diameter are declared as a signed int, but you're trying to do floating point. The compiler is going to truncate 31.249 to 31 and do an integer calculation. 

You are very much right.

circumference = 31.429*diameter;

diameter= 300; and I have shifted decimal one digit right to the value of Pi. Result on RS232 output gives 9428 ( should have been 9428.7)

circumference = 300mm*Pi = 942.87 is the right value. I get 9428 which meets my requirement.

Tried with different diameter values.

Can any one throw light on this floating point Calc in AVR where one has declared quantities as signed Integer. So we know our limitations.

Any way thanks for enlightening me as I am self taught and hence prone to errors (probably because I presume)

Yes I2C communication in Industrial environment but within the same metal tube housing. May be CAN would help but IC count increases in the housing.